Human African trypanosomiasis (HAT) is caused by the parasitic protozoan Trypanosoma brucei. HAT exerts a large burden in both health and economic costs to the affected regions. There is a great need to translate recent advances in the understanding ofthe basic biology ofthe parasite into new drugs. Polyamines are essential metabolites that are required for cell growth. The polyamine biosynthetic enzymes, including ornithine decarboxylase (ODC) and S-adenosylmethionine decarboxylase (AdoMetDC) are essential to the parasite, and ODC is the target of a currently utilized anti-trypanosomal drug called eflornithine. In order to better understand the pathway and its potential to be exploited for additional drug discovery my lab has been using genetic, biochemical and structural approaches to determine which enzymes in the pathway are essential, to characterize regulatory mechanisms used to control pathway flux, to understand structure function relationships influencing catalysis and ligand binding to ODC and AdoMetDC, and to discover new inhibitors of pathway enzymes. In this fund period we have shown that spermidine synthase and glutathione synthase are essential enzymes, we have built on our previous discovery that that AdoMetDC is regulated by a novel mechanism by identifying both cis and trans factors that may contribute to translational regulation ofthe AdoMetDC regulatory subunit prozyme and we have identified new inhibitors of both ODC and AdoMetDC. Finally in a new direction we have begun studies on the role of deoxyhypusine synthase (DHS) in T. brucei. We remarkedly discovered that similarly to AdoMetDC, DHS is activated by oligomerization with a catalytically dead paralog, showing that this novel mechanism has evolved twice within the trypanosomatid polyamine metabolic pathway. Future studies will build on these findings to: 1) characterize cis/trans regulatory factors influencing translation of prozyme, 2) solve the X-ray structure sof both the AdoMetDC and DHS 3) identify other proteins in T. brucei that are regulated by inactive paralogs, and 4) study the role of deoxyhypusine modification of elF5A in T. brucei. RELEVANCE (See instructions): Human African sleeping sickness is a fatal insect borne disease and current drug therapies are toxic and difficult to administer. The work described in this proposal characterizes the biology of an essential metabolic pathway (polyamine and trypanothione biosynthesis) that has unique features in the parasite, with the goal of providing insight into the potential to target this pathway for drug discovery.